1. Field of the Invention
The present invention relates to a wireless power supply system, a power transmission device, and a power receiving device. The present invention particularly relates to a wireless power supply system including a power transmission device capable of wirelessly supplying power to a plurality of power receiving devices, and a power transmission device and a power receiving device that are applicable to the wireless power supply system.
2. Description of the Related Art
Four methods are known for supplying power in a contactless (wireless) manner: an electromagnetic induction method, a magnetic field resonance method, an electric field coupling method, and a radio wave receiving method. In recent years, among these four methods, the magnetic field resonance method has attracted attention because of its capabilities of transmitting a large amount of power and transmitting power over a long distance. For example, Japanese Patent Application Laid-Open No. 2009-136132 discusses a one-to-N (N is a natural number of two or more) power supply system for transmitting power from a power transmission device to a plurality of wireless power receiving devices by utilizing the magnetic field resonance method having the long-distance power transmission capability.
Further, Japanese Patent Application Laid-Open No. 2012-44735 discusses a method for detecting an abnormality in a power transmission path between one power transmission device and N wireless power receiving devices.
In the configuration discussed in Japanese Patent Application Laid-Open No 2009-136132, during standby without supplying power, the power transmission device transmits a predetermined pulse signal to search for any wireless power receiving device that is close within several meters of the power transmission device. When the wireless power receiving device transmits its own unique identification (ID) to the power transmission device, the power transmission device determines whether the wireless power receiving device is a target to be power supplied. If the wireless power receiving device is a target to be power supplied, the power transmission device wirelessly transmits power to the wireless power receiving device. At this point, the power transmission device can transmit a unique code to the wireless power receiving device to individually receive information about the amount of charge and the status of the device.
In the configuration discussed in Japanese Patent Application Laid-Open No. 2012-44735, the presence of any foreign matter between the power transmission device and the power receiving device is detected by using a sensor or a heating sensor to perform control so that the power receiving device cannot receive power on its side when the foreign matter has been detected.
In a configuration such as that discussed in Japanese Patent Application Laid-Open No. 2012-44735, an operation is performed to stop supplying power when an abnormality has been detected. More specifically, a secondary side device (power receiving device) includes a sensor for detecting an abnormality, and according to the detection result by the sensor, transmission and reception of power is stopped so that heating due to foreign matter can be avoided. However, in such a configuration, if power is not normally supplied due to a cause other than the foreign matter, it cannot be determined whether the cause is on the power supply device side or on the power receiving device side.